The present invention relates to a fuel injection pump for delivering fuel under high pressure to a plurality of cylinders of an internal combustion engine, and more specifically to a fuel injection pump designed so that when highly pressurized or compressed fuel is delivered from a pump chamber of the fuel injection pump toward one of the engine cylinders, the fuel delivery can be adjusted by spilling the compressed fuel to a low-pressure region on the side of a fuel tank by means of a solenoid valve, thereby bringing the delivery of the compressed fuel to an end.
A conventional fuel injection pump of this type, for example, a fuel supply system for an internal combustion engine is described in Japanese Patent Publication No. 34936/76.
A solenoid valve to be used in the fuel injection pump of this type can be controlled for its valve-opening time in accordance with the operating conditions of the engine, such as engine load, speed, etc. In the fuel injection pump with the solenoid valve for controlling the delivery of compressed fuel, therefore, the fuel delivery can be adjusted to an optimum level for operating the engine.
Despite these advantages, the fuel injection pump of this type has some drawbacks. For example, if the solenoid of the solenoid valve suffers disconnection, or if a drive circuit for the solenoid valve gets out of order, the solenoid will not be able to be controlled normally, that is, the solenoid valve will fail to open correctly at predetermined times. In such a case, all the compressed fuel pressurized by a pump plunger in a pump chamber of the fuel injection pump will be delivered toward one of the engine cylinders. In other words, the compressed fuel will be delivered from the pump chamber for the whole compression stroke of the pump plunger used in the compression of the fuel in the pump chamber. Specifically, in case of such a problem, the fuel delivery to the engine cylinders will be 1.5 to 2 times as great as the maximum fuel delivery obtained with the normal control of the solenoid valve. Accordingly, the engine will suffer an undue increase of the rotational frequency, as well as producing an extraordinary amount of black smoke in its exhaust gas.